The present invention relates to a solid component of catalyst, the procedure for its preparation and its use in procedures for the (co)polymerization of ethylene and xcex1-olefins.
It is well-known that ethylene, or xcex1-olefins in general, can be polymerized by means of a procedure at low pressure on Ziegler-Natta catalysts. These catalysts are generally composed of a compound of elements from sub-group IV to VI of the periodic table (compounds of transition metals), mixed with an organometallic compound, or hydride, of the elements belonging to group I to III of the periodic table.
Solid components of Ziegler-Natta catalysts are also known, containing a transition metal (generally titanium), a bivalent metal (generally magnesium), a halogen (generally chlorine) and also possibly an electron donor. These solid components, used in combination with an organometallic compound of aluminium, form active catalysts for the (co)polymerization of ethylene in procedures carried out at low temperature and pressure. U.S. Pat. No. 3,642,746, for example, describes a solid component of catalyst obtained by the contact of a compound of a transition metal with a halide of a bivalent metal treated with an electron donor. According to U.S. Pat. No. 4,421,674 a solid component of catalyst is obtained by the contact of a compound of a transition metal with the product of a solution of magnesium chloride in ethanol which has been spray-dried.
According to U.K. Patent 1.401.708 a solid component of catalyst is obtained by the interaction of a magnesium halide, a non-halogenated compound of a transition metal and an aluminium halide. U.S. Pat. Nos. 3,901,863 and 4,292,200 describe solid components of catalyst obtained by putting a non-halogenated compound of magnesium in contact with a non-halogenated compound of a transition metal and an aluminium halide.
U.S. Pat. No. 4,843,049 and European Patent Application publication 243.327 describe solid components of catalyst which contain titanium, magnesium, aluminium, chlorine and alkoxy groups, highly active in procedures for the (co)polymerization of ethylene carried out at low pressure and temperature, using the technique of suspension, and at high pressure and temperature respectively, in vessels or tubular reactors. These solid components are generally obtained by spray-drying an ethanol solution of magnesium chloride to obtain an active support, which is subsequently reacted with a titanium tetraalkoxide or with titanium tetrachloride and an alkyl aluminium chloride respectively.
It has now been found, according to the present invention, that by introducing magnesium-carboxylate bonds and a transition metal-carboxylate, generally improved solid components of catalyst are obtained, compared to those of the known art, with respect to their highly developed activity in procedures for the (co)polymerization of ethylene and xcex1-olefins carried out at low pressure and temperature, at high pressure and temperature and in solution and also to the nature of the polymers thus obtained.
In accordance with this, the first aspect of the present invention relates to a solid component of catalyst for the (co)polymerization of ethylene and xcex1-olefins which contains magnesium-carboxylate bonds and a transition metal-carboxylate and which can be represented by the formula:
M1Mg(0.3-20)X(2-60)Al(0-6)(Rxe2x80x94COO)(0.1-3)xe2x80x83xe2x80x83(I)
wherein:
M is at least one metal selected from titanium, vanadium, zirconium and hafnium,
X is a halogen excluding iodine, and
R is an aliphatic, cycloaliphatic or aromatic hydrocarbon radical, containing at least 4 carbon atoms.
According to one embodiment, the metal M in formula (I), represents titanium, or titanium and another metal selected from zirconium and hafnium in an atomic ratio between titanium and the other metal of 0.25:1 to 2.0:1 and preferably 0.33:1 to 1:1.
In another preferred embodiment, the halogen X, in formula (I), represents chlorine or bromine and in the more preferred form chlorine.
The maximum number of carbon atoms of the radical R, in formula (I) is not particularly critical, however it is generally not advisable to exceed a value of 25.
Another aspect of the present invention relates to a procedure for the preparation of the solid component of catalyst (I) which includes:
(i) the formation of a solution, in an inert organic solvent, of a magnesium carboxylate or halide of magnesium carboxylate:
MgXn(Rxe2x80x94COO)(2xe2x88x92n)xe2x80x83xe2x80x83(II)
xe2x80x83and at least one transition metal carboxylate or halide of at least one transition metal carboxylate:
MXm(Rxe2x80x94COO)(4xe2x88x92m)xe2x80x83xe2x80x83(III)
xe2x80x83wherein:
M is at least a metal selected from titanium, vanadium, zirconium and hafnium,
X is a halogen excluding iodine,
R is an aliphatic, cycloaliphatic or aromatic hydrocarbon radical, containing at least 4 carbon atoms, up to about 25 carbon atoms,
n varies from 0 to 1, and
m varies from 0 to 2, and wherein the atomic ratio between the magnesium in (II) and the transition metal (M) in (III) is within the range of 0.3:1 to 20:1;
(ii) the addition to the solution of step (i) of an alkyl aluminium halide having the formula:
AlRxe2x80x2pX(3xe2x88x92p)xe2x80x83xe2x80x83(IV)
xe2x80x83wherein:
Rxe2x80x2 is a linear or branched alkyl radical, containing from 1 to 20 carbon atoms, and
X is a halogen atom excluding iodine, and wherein the ratio between the halogen atoms in (IV) and the total carboxy groups in (II) and (III) varies from 0.3:1 to 10:1, to precipitate the solid component of catalyst (I) into a solid granular form, and
(iii) the recovery of the solid component of catalyst from the reaction products of step (ii).
The solvent used to prepare the solution in step (i) of the procedure, may be any inert (not reactive) organic solvent towards the other constituents. Preferred solvents for the purpose are aliphatic, cycloaliphatic or aromatic hydrocarbon solvents, liquid in the operating conditions, such as hexane, heptane, octane, nonane, decane, undecane, dodecane, cyclopentane, cyclohexane, benzene, toluene, xylenes and mesithylenes.
Examples of Rxe2x80x94COO carboxylic groups, in formulae (II) and (III), are those wherein:
the radical R is a linear alkyl containing at least 9 carbon atoms; for example n-decanoate, n-undecanoate and n-dodecanoate groups;
the radical R is a branched alkyl product having a branching on the secondary carbon atom in xcex1 with respect to the carboxyl carbon: 
wherein the sum of carbon atoms in R1 and R2 is equal to at least 2; for example isobutyrate groups, 2-methylbutyrate groups and 2-ethylhexanoate groups;
the radical R is a branched alkyl having two branchings on the tertiary carbon atom in xcex1 with respect to the carboxyl carbon 
wherein the sum of the carbon atoms in R3, R4 and R5 is equal to at least 3; for example 2,2-dimethyl propanoate and versatate groups;
the radical R is an alkyl having a branching on the secondary carbon atom in xcex2 position with respect to the carboxyl carbon atom: 
wherein the sum of the carbon atoms in R6 and R7 is equal to at least 4; for example 3-ethyl pentanoate and citronellate groups;
the radical R is a cycloalkyl, cycloaryl, alkylene cycloalkyl or alkylene cycloaryl:
Raxe2x80x94(CH2)axe2x80x94COO
wherein R8 represents the cycloalkyl or cycloaryl portion, either monocyclic or with several condensed or uncondensed cycles, and s varies from 0 to 10; for example the naphthenate group;
the radical R is an alkyl substituted with aryl in position xcex1 with respect to the carboxyl carbon atom: 
wherein R9 is an aryl, for example a phenyl and R10 is an alkyl containing at least 1 carbon atom; for example the 2-phenylbutyrate group.
In accordance with one embodiment, the metal M, in formula (III), represents titanium, or titanium and another metal selected from zirconium and hafnium, with an atomic ratio between the titanium and the other metal of 0.25:1 to 2.0:1 and preferably 0.33:1 to 1:1.
In another preferred embodiment, X, in formulae (II) and (III), represents chlorine or bromine and in the preferred form chlorine.
In accordance with a further embodiment, n in formula (II) has a value of at least 0.1 and preferably at least 0.5 to 1, and m in the formula (III) has a value of at least 0.1 and preferably at least 0.2 to 2.
It is convenient in step (i) to mix a solution of compound (II) in the selected solvent, with a solution of compound (III) in the same solvent, or in a different solvent, operating at room temperature (20-25xc2x0 C.) or at temperatures close thereto. The solutions of compounds (II) and (III) in the relative solvents can be obtained with a simple and practical procedure, which will be described hereinbelow and illustrated in the examples.
In step (ii) of the procedure, an aluminium halide (IV) is added to and reacted with the solution prepared in step (i). Preferred aluminium halides are alkyl aluminium chlorides and bromides, wherein the alkyl contains from 1 to 6 carbon atoms. Aluminium halides which are even more preferred are ethyl aluminium dichloride, diethyl aluminium chloride, ethyl aluminium sesquichloride, isobutyl aluminium dichloride, diethyl aluminium bromide and ethyl aluminium dibromide. The aluminium halide may be added as such, or in the form of a solution in an inert organic solvent selected from those used for the preparation of the solution of step (i).
In step (ii) it is convenient to operate at a temperature ranging from 20 to 120xc2x0 C. for a period which, depending on the temperature selected, may vary from 0.5 to 8 hours. In the preferred method, the aluminium halide is added to the solution of compounds (II) and (III), at room temperature (20-25xc2x0 C.), or at a temperature close thereto and the mixture obtained is heated to a temperature ranging from 50 to 100xc2x0 C., for a period of 45 to 180 minutes.
Operating under these conditions, the solid component of catalyst (I) is obtained in the form of a powder precipitate, with a particle size of 10 xcexcm to 40 xcexcm. When M represents titanium, catalysts (I) are obtained wherein the ratio between titanium in its trivalent state and the sum of titanium in its trivalent and tetravalent state generally varies from 0.9:1 to 1:1.
The solid component of catalyst thus obtained is separated from the suspension in step (iii) using normal methods such as decantation, filtration or centrifugation, washed with a hydrocarbon solvent and possibly dried.
As specified before, compounds (II) and (III) can be prepared directly in solution using a simple and practical method. More specifically, compounds (II) can be obtained by the reaction of a Rxe2x80x94COOH carboxylic acid (wherein R corresponds to the above definition) with a magnesium halide MgX2 (wherein X has the above definition), in accordance with the following reaction:
MgX2+(2xe2x88x92n)Rxe2x80x94COOHxe2x86x92MgXn(Rxe2x80x94COO)(2xe2x88x92n)+(2xe2x88x92n)HCl
Similarly compounds (III) can be obtained by the reaction of a Rxe2x80x94COOH carboxylic acid (wherein R has the above definition) with a halide of a metal M (MX4, wherein X has the above definition), in accordance with the reaction:
MX4+(4xe2x88x92m)Rxe2x80x94COOHxe2x86x92MXm(Rxe2x80x94COO)(4xe2x88x92m)+(4xe2x88x92m)HCl
Examples of suitable Rxe2x80x94COOH acids are n-decanoic, n-undecanoic, n-dodecanoic, 2-ethylhexanoic, versatic, citronellic, naphthenic and 2-phenyl-butyric acids.
The magnesium halide used for the purpose may be:
a highly crystalline magnesium halide, with a particle size preferably not higher than 100 xcexcm and with a water content preferably lower than 0.2% by weight; or
a partially or completely amorphous magnesium halide, such as that which can be obtained by the prolonged grinding of a crystalline magnesium halide or by the spray-drying of aqueous solutions or solutions in an organic solvent of a magnesium halide.
Among all magnesium halides, it is preferable to use amorphous magnesium chloride obtained by the spray-drying of ethanol solutions of the chloride, as described for example in U.S. Pat. No. 4,843,049.
The reaction between magnesium halide or the halide of metal M and Rxe2x80x94COOH acid is conveniently carried out in an inert organic solvent and preferably an aliphatic, cycloaliphatic or aromatic solvent, by eliminating the hydrologenic acid which develops as a reaction by-product, for example by bubbling a flow of an inert gas such as nitrogen. At the end of the reaction, a solution of magnesium halide carboxylate or metal M halide carboxylate is obtained in a dissolved form in the solvent used as reaction medium. The solvent will obviously be selected so as to have the maximum solubility of the reagents and reaction products. Paraffinic solvents will therefore be preferred when aliphatic Rxe2x80x94COOH acids are used and aromatic, solvents when aromatic or substantially aromatic Rxe2x80x94COOH acids are used. The use of mixed solvents is obviously not excluded. Whatever the case, any possible undissolved material may be separated by filtration or decanting. In the preparation of compound (II) it is convenient to operate with concentrations of MgX2 of 0.1 to 0.7M, in that with higher concentration values a decrease is observed in the yield of the desired compound (II). On the other hand, the concentration of compounds MX4 in the preparation of compound (III) is not particularly critical. If there is an excess of Rxe2x80x94COOH acid in the mixture at the end of the reaction, it is not necessary to separate this, provided that the free carboxylic groups do not exceed 100% of the solified total carboxylic groups. If this is the case in step (ii) of the procedure for the preparation of the solid component of catalyst, the total carboxylic groups will be those deriving from (II) and (III) and those deriving from free Rxe2x80x94COOH acid.
When a magnesium chloride spray-dried from an alcohol solution, particularly an ethanol solution, is used in step (i), the solid component of catalyst (I) will additionally contain alkoxy groups, and in particular ethoxy groups, in quantities, however, not higher than 25% with respect to the total carboxy groups.
In a preferred embodiment, the solution used in step (i) of the procedure for the preparation of the solid component of catalyst is obtained by the reaction of a solution containing both MgX2 and MX4, with the required quantity of Rxe2x80x94COOH acid. However, a separate reaction, as described above, is generally preferred, in that it is a more versatile method of obtaining components of catalyst with different formulations.
A further aspect of the present invention relates to catalysts for the (co)polymerization of ethylene and xcex1-olefins, formed from the solid component of catalyst described above, combined with an organo-metallic compound of aluminium (co-catalyst) which can be selected from aluminium trialkyls and the halides (such as chlorides) of aluminium alkyl, containing 1 to 6 carbon atoms in the alkyl portion. Among these, aluminium trialkyls are preferred, such as aluminium triethyl, aluminium tri-n-butyl, aluminium triisobutyl and aluminium trihexyl. In the catalysts of the present invention the atomic ratio between the aluminium (in the co-catalyst) and the titanium (in the solid component of catalyst) generally varies from 3:1 to 1,500:1 and preferably from 5:1 to 200:1, in relation to the particular polymerization system used and its purity.
The present invention also relates to procedures for the polymerization and copolymerization of ethylene and xcex1-olefins which use the above catalyst. The xcex1-olefins are generally those containing from 3 to 15 carbon atoms, such as propylene, butene-1, 4-methylpentene-1, hexene-1 and octene-1.
In particular, the catalyst of the present invention may be used in the preparation of polyethylenes with a narrow molecular weight distribution, which have the desired combination of characteristics as regards Melt-Index, Shear Sensitivity and ratio between weight average molecular weight (Mw) and number average molecular weight (Mn). In this case, it is convenient to operate using the technique of a suspension in an inert diluent under the following general conditions: temperature 60 to 95xc2x0 C., pressure 6 to 20 kg/cm2 and ratio between the partial pressures of hydrogen and ethylene of 0 to 5. In the homopolymerization of ethylene and copolymerization of ethylene with propylene, butene-1 or hexene-1, to obtain polyethylenes with a narrow molecular weight distribution (Mw/Mn from 3 to 6), it is preferably to use solid components of catalyst with a lower content of magnesium and halogen, wherein M is titanium (IA):
M1Mg(0.3-2.0)X(2.0-6.0)Al(0.1-0.5)(Rxe2x80x94COO)(1.53-3)
These solid components of catalyst may be obtained by operating under the general conditions of the above procedure and using in step (i) an atomic ratio between magnesium and transition metal tending towards the lower limits, such as for example 0.3:1 to 2.0:1 and a ratio between the halogen atoms and carboxy groups in step (ii) towards low limits such as 0.3:1 to 1.5:1.
The solid component (IA) is also suitable for the copolymerization of ethylene with xcex1-olefins, especially propylene, giving copolymers with elastomeric characteristics. In this case, it is convenient to use the method in suspension or solution, at a temperature of 20 to 60xc2x0 C. and a pressure of 4 to 25 kg/cm2.
When it is necessary to produce a (co)polymer of ethylene with a wide distribution of molecular weight in a two-step procedure in suspension, it is advantageous to use solid components of catalyst with an average content of magnesium and halogen, wherein M is preferably titanium (IB):
M1Mg(1.0-3.0)X(4.5-12)Al(0.5-1.5)(Rxe2x80x94COO)(0.5-1.0)
These solid components of catalyst may be obtained by operating under the general conditions of the above procedure and using in step (i) an atomic ratio between magnesium and transition metal of 1.0:1 to 3.0:1 and a ratio between the halogen atoms and carboxy groups in step (ii) towards the lower limits such as 1.2:1 to 4.0:1. In this case, it is convenient to operate at temperatures of 70 to 90xc2x0 C. for the first step, with total pressures of 8 to 12 kg/cm2 and at temperatures of 70 to 90xc2x0 C. for the second step, with total pressures of 4 to 8 kg/cm2 and with a ratio between the partial pressures of hydrogen and ethylene of 0.15 to 4.5.
For the production of an ethylene polymer with a wide distribution of molecular weights in a one step procedure in suspension, it is advantageous to use a solid component of catalyst wherein M represents two transition metals and preferably titanium and zirconium or hafnium with an atomic ratio Ti:Zr or Ti:Hf of 0.33:1 to 1:1 (IC):
M1Mg(0.5-2.5)X(5-10)Al(0-1)(Rxe2x80x94COO)(0.1-0.4)
This bimetallic catalyst can be easily obtained by using, in step (i) of the procedure a solution of titanium chloride carboxylate and a solution of zirconium or hafnium chloride carboxylate. The polymerization is conveniently carried out in one step, using the suspension method, at a temperature of 70 to 95xc2x0 C., at a pressure of 6 to 15 kg/cm2 and with a ratio between the partial pressures of hydrogen and ethylene of 0 to 5. The molecular weight distribution of the polyethylenes obtained with the one step procedure can be controlled by varying the composition of the bimetallic component of catalyst, within the above limits, and/or by introducing a Lewis base, as described in Italian Patent Application 22.115 A/88, of Sep. 29th 1988 in the name of the Applicant.
The solid component of catalyst of the present invention is also highly active in procedures for the copolymerization of ethylene with xcex1-olefins, carried out at a high temperature and pressure, in vessel or tubular reactors, to obtain LLDPE (density from 0.935 to 0.915 g/ml), and VLLDPE (density from 0.915 to 0.900 g/ml) and ULDPE (density from 0.900 to 0.87). In these procedures it is customary to operate at temperatures of 90xc2x0 C. to 280xc2x0 C., at pressures of 800 to 2,000 kg/cm2 and for 15 to 90 seconds in the case of tubular reactors and at temperatures of 140 to 280xc2x0 C., with times of 45 to 180 seconds and at pressures similar to those specified above, in the case of vessel reactors. In these polymerizations, it is preferable to use solid components of catalyst with a higher content of magnesium and halogen, wherein M is preferably titanium or titanium and hafnium. When M is titanium the solid component of catalyst can be defined with the formula (ID):
M1Mg(7-20)X(15-60)Al(0-6)(Rxe2x80x94COO)(0.4-3)
When M is titanium and hafnium, in an atomic ratio of 0.33:1 to 1:1, the formula for the preferred catalyst is (IE):
M1Mg(2-3.5)X(8-12)Al(0-2)(Rxe2x80x94COO)(0.1-0.4)
It has been found that the solid components of catalyst (ID) and (IE) are active in catalysts wherein the atomic ratio between the aluminium (in the co-catalyst) and the titanium (in the solid component of catalyst) is unusually low and in particular within the range of 3 to 10 and are capable of producing copolymers of ethylene with butene-1 and with propylene having a high molecular weight (not sticky) and density values as low as 0.870 g/ml.
Finally, the solid component of catalyst of the present invention is highly active in procedures for the homopolymerization of xcex1-olefins such as propylene, butene-1, 4-methyl-1-pentene, hexene-1 and octene-1, to obtain poly(xcex1-olefins) with a high productivity and high molecular weight, in relation to the composition of the component itself. In particular, in order to produce poly(xcex1-olefins) with a high productivity, it is advantageous to use solid components of catalyst with a high content of magnesium wherein M is titanium (IF):
M1Mg(7-20)X(15-60)Al(0-4)(Rxe2x80x94COO)(0.4-3.0)
To produce poly(xcex1-olefins) with a high molecular weight (ultra high molecular weight) in the above formula (IF) M will represent hafnium or zirconium. In both cases the polymerization will be carried out in suspension, at temperatures ranging from 20 to 90xc2x0 C.
The following reference examples and examples for the preparation of catalyst and for polymerization provide a better illustration of the present invention. In reference examples 1 to 19, a magnesium chloride is used, which is obtained by spray-drying an ethanol solution of magnesium chloride, in the form of spherical particles, of which about 90% have a size of 0.5 to 10 xcexcm, with an apparent density of 0.4 g/ml, surface area of 3 m2/g, porosity of 0.7 ml/g and content of hydroxy groups from alcohols of 10% by weight (expressed as weight of ethanol). This magnesium chloride was obtained in accordance with Example 1 of U.S. Pat. No. 4,843,049.